1. Field of the Invention
The present invention relates to a turning bar apparatus disposed in a running path of a web and adapted to change the running direction of the web.
2. Description of the Related Art
Conventionally, air outlet openings are formed in a turning bar disposed in a web path, in order to cause a web looped around the turning bar to float above the outer circumferential surface of the turning bar by means of air discharged therethrough. Such a turning bar is disclosed in, for example, Japanese Utility Model Application Laid-Open (kokai) Nos. 5-28632 "Turning bar Apparatus" and 5-32353 "Web Guide Roll" and Japanese Patent Application Laid-Open (kokai) No. 6-345306 "Turning Bar."
FIG. 6 shows the turning bar apparatus (hereinafter, called the first conventional art) disclosed in Japanese Utility Model Application Laid-Open (kokai) No. 5-28632. As shown in FIG. 6, a turning bar 30 of the turning bar apparatus includes an exterior pipe 32 having a hollow space 31 formed therein. A number of air outlet openings 33 are formed in the exterior pipe 32 so as to extend from the hollow space 31 to the outer circumferential surface of the exterior pipe 32, which comes into contact with a web W.
The air outlet openings 33 are positioned in the circumferential direction of the exterior pipe 32 at: a web-looping-region upstream-end-portion 34 of the turning bar 30; a web-looping-region downstream-end-portion 35 of the turning bar 30; a web-looping-region center-portion 39 located at the center between the web-looping-region upstream-end-portion 34 and the web-looping-region downstream-end-portion 35; a web-looping-region upstream-portion 37 extending between the web-looping-region upstream-end-portion 34 and the web-looping-region center-portion 39; and a web-looping-region downstream-portion 38 extending between the web-looping-region downstream-end-portion 35 and the web-looping-region center-portion 39. In each of the positions, a plurality of air outlet openings 33 are arranged in a row along the longitudinal direction of the turning bar 30.
The turning bar 30 is disposed in a web path of a rotary press. Compressed air supplied to the hollow space 31 is discharged through the air outlet openings 33 formed in the turning bar 30 so as to cause the web W to float above the outer circumferential surface of the exterior pipe 32, thereby preventing blurred printing which might otherwise result from rubbing or contact between the web W and the outer circumferential surface of the turning bar 30.
Japanese Utility Model Application Laid-Open (kokai) No. 5-28632 (hereinafter, called the second conventional art) also discloses a turning bar apparatus improved from the turning bar apparatus of the first conventional art. According to the second conventional art, an air duct is disposed on the side of the exterior pipe 32 where the web W does not contact the exterior pipe 32. Compressed air is supplied to the air duct. Nozzles are attached to the air duct so as to discharge compressed air therethrough in a direction tangent to the exterior pipe 32 toward the web-looping-region upstream-end-portion 34, where the web W begins to be looped around the exterior pipe 32, and toward the web-looping-region downstream-end-portion 35, where the web W leaves the exterior pipe 32. According to the second conventional art, through discharge of compressed air through the nozzles, the web W is caused to be floated farther above the outer circumferential surface of the exterior pipe 31.
According to Japanese Patent Application Laid-Open (kokai) No. 6-345306 (hereinafter, called the third conventional art), as shown in FIGS. 8A and 8B, a turning bar 2 for changing the running direction of a web 1 by substantially a right angle is disposed in combination with an upstream guide roller 13 and a downstream guide roller 14. The upstream guide roller 13 is adapted to lead the web 1 toward the turning bar 2 and is disposed upstream of the turning bar 2 with respect to the direction of travel of the web 1 such that an axis level thereof is equal to that of the turning bar 2 and such that phase thereof differs 45 degrees from that of the turning bar 2. The downstream guide roller 14 causes the web 1 to separate from the turning bar 2 and is disposed downstream of the turning bar 2 such that an axis level thereof is equal to that of the turning bar 2 and such that phase thereof differs 45 degrees from that of the turning bar 2 and 90 degrees from that of the upstream guide roller 13.
At least three rows of nozzles 5 are arranged on the surface of the turning bar 2 along the longitudinal direction of the turning bar 2 over a length corresponding to the width of the web 1, as well as within a circumferential web-looping region of the turning bar 2. The nozzles 5 are arranged at longitudinally equal intervals over a portion or the entirely of the length corresponding to the width of the web 1. Central angles defined by adjacent rows of nozzles 5 are equal to each other. An additional row of nozzles 5 is arranged longitudinally inward and at greater density than are the three rows of nozzles 5 on the surface of the turning bar 2 over an appropriate length from a portion of the turning bar 2 corresponding to a web side edge portion at which the length of the web 1 extending between the upstream guide roller 13 and the turning bar 2 is shorter than that as measured at the other web side edge. Similarly, an additional row of nozzles 5 is arranged longitudinally inward and at greater density than are the three rows of nozzles 5 on the surface of the turning bar 2 over an appropriate length from a portion of the turning bar 2 corresponding to a web side edge portion at which the length of the web 1 extending between the downstream guide roller 14 and the turning bar 2 is shorter than that as measured at the other web side edge. Through such arrangement of nozzles 5, compressed air is supplied in greater amount to a portion of the web 1 which would otherwise be floated to a lesser extent, thereby establishing sufficient floating of the web 1 over the length of the turning bar 2.
As shown in FIGS. 9A and 9B, a web guide roll 2 (hereinafter, called the fourth conventional art) disclosed in Japanese Utility Model Application Laid-Open (kokai) No. 5-32353 is used for changing the running direction of a web 1 while the web 1 is floated above the surface thereof by means of air. A plurality of small holes 4 are formed in a web-looping region of the web guide roll 2 so as to discharge air therethrough for floating the web 1. The small holes 4 are distributed on the web guide roll 2 circumferentially within a range from the position where the web 1 begins to be looped around the web guide roll 2, to the position of a quarter circumference. In addition to the small holes 4, Coanda-type slits 5 (or a row of Coanda-type small holes 5') are formed for discharging air therethrough.
On the upstream side of a region of distributed small holes 4, a longitudinal Coanda-type slit 5 or a row of Coanda-type small holes (not shown) is arranged along the axial direction of the guide roll 2 such that air is discharged therethrough in an inclined manner so as to follow travel of the web 1. On the downstream side of the region of distributed small holes 4, a longitudinal Coanda-type slit 5 or a row of Coanda-type small holes (not shown) is arranged along the axial direction of the guide roll such 2 that air is discharged therethrough in an inclined manner so as to flow against travel of the web 1. Circumferential Coanda-type slits 5' are formed on the opposite sides of the region of distributed small holes 4 with respect to the web-width direction such that air is discharged therethrough in an inclined manner so as to flow inward with respect to the axial direction of the guide roll 2.
Through discharge of air from the Coanda-type slits 5' and a row of Coanda-type small holes (not shown) and from the Coanda-type slits 5', the ratio of the amount of escaping air to the amount of air discharged from the small holes 4 is reduced, thereby enhancing floating of the web 1.
However, the above-described conventional arts involve the following problems.
In the turning bar apparatus according to the first and second conventional arts, as shown in FIG. 6, a floating force exerted by air discharged from the air outlet openings 33 arranged longitudinally along the turning bar 30 at the web-looping-region center-portion 39 is directed against a resultant force of a tension T of a web W1 which runs toward the turning bar 30 and a tension T of a web W2 which leaves the turning bar 30. Thus, the floating force is directly subjected to the resultant force; i.e., 2T. As the web tensions T increase, the gap between the web W and the surface of the exterior pipe 32 decreases as shown in FIG. 7A; i.e., the web tensions T function toward blocking the air outlet openings 33.
As a result, as in the case where blowing cellophane paper under tension causes vibration of the paper, the web W jitters across its width. Such jittering causes the web W to move widthwise, or to undergo transverse paper shift. Jittering of the web W increases with the pressure of compressed air 36, causing not only transverse paper shift but also imposition of an unnecessarily strong tension on the web W with resultant unstable travel of the web W.
Also, as shown in FIG. 6, at the web-looping-region upstream-end-portion 34 and at the web-looping-region downstream-end-portion 35, a floating force exerted by air discharged from the longitudinally arranged air outlet openings 33 is directed substantially perpendicular to the tension T of the web W1 and to the tension T of the web W2, respectively. Thus, a force for pressing the web W1 (W2) toward the air outlet openings 33 is not directly influenced by the web tension T.
That is, since no force is generated for pressing toward the air outlet openings 33 the web W1 running toward the turning bar 30 and the web W2 leaving the turning bar 30, travel of the web W becomes unstable. Particularly, when the web tensions T are weak, the compressed air 36 is discharged against the web W which is running unstably, causing the web W to flutter. The fluttering web W closes and opens in an irregular manner the longitudinally arranged air outlet openings 33. As a result, air flow balance within the gap between the web W and the outer circumferential surface of the exterior pipe 32 tends to be destroyed with respect to the web width direction, although air flow balance is maintained with respect to the circumferential direction of the turning bar 30. Thus, the web W is likely to move widthwise.
Increased supply of the compressed air 36 causes unnecessarily intensive floating of the web W, causing increased fluttering of the web W. Thus, travel of the web W becomes more unstable.
Therefore, since the supply of the compressed air 36 is must be decreased, the web W fails to float sufficiently, causing rubbing between the turning bar 30 and the web W with resultant blurred printing. Further, the air outlet openings 33 may become clogged with ink and paper dust.
In the turning bar according to the third conventional art, a number of nozzles are arranged at a portion of the turning bar which is in contact with the web. Further, since a row of nozzles is arranged along the axial direction of the turning bar at the circumferential center of the web-looping region, the turning bar causes a phenomenon similar to the phenomenon induced by a row of air outlet openings arranged at the web-looping-region center-portion 39 in the first and second conventional arts.
Also, nozzles are arranged at greater density at portions of the turning bar corresponding to side edge portions of the looped web than at an intermediate portion of the turning bar. As in the case shown in FIG. 7B, air discharged from those nozzles which are located in correspondence with the side edge portions of the web may turn up the side edge portions of the web, thereby disturbing a floating state of the web. As a result, air flow balance within the gap between the web and the web-looping region of the turning bar tends to be destroyed with respect to the web width direction, while air flow balance is rather maintained with respect to the circumferential direction of the turning bar. Thus, the web is likely to move widthwise. Particularly, when the supply of compressed air is increased, the side edge portions of the web become more likely to be turned up; thus, the web becomes more likely to move widthwise.
Therefore, since the supply of compressed air must be decreased, the web fails to float sufficiently, causing rubbing between the turning bar and the web with resultant blurred printing. Further, the nozzles may become clogged with ink and paper dust.
In the guide roll (turning bar) according to the fourth conventional art, at a portion of the guide roll where the web begins to be looped around the guide roll and at a portion of the guide roll where the web leaves the guide roll, a floating force exerted by air discharged from the longitudinally arranged air outlet holes is directed substantially perpendicular to tension associated with the approaching web and to tension associated with the leaving web, respectively. Thus, a force for pressing the web toward the air outlet holes is not directly influenced by the web tension.
That is, since no force is generated for pressing toward the air outlet holes the web running toward the guide roll and the web leaving the guide roll, travel of the web becomes unstable. Particularly, when the web tension is weak, compressed air is discharged against the web which is running unstably, causing the web to flutter. The fluttering web closes and opens in an irregular manner the longitudinally arranged air outlet holes. As a result, air flow balance within the gap between the web and the web-looping region of the guide roll tends to be destroyed with respect to the web width direction, while air flow balance is rather maintained with respect to the circumferential direction of the guide roll. Thus, the web is likely to move widthwise. Increased supply of compressed air causes unnecessarily intensive floating of the web, causing increased fluttering of the web. Thus, travel of the web becomes more unstable.
Also, as in the case shown in FIG. 7B, air discharged from those nozzles which are located at portions of the guide roll corresponding to the side edge portions of the web may turn up the side edge portions of the web, thereby disturbing a floating state of the web. As a result, air flow balance within the gap between the web and the web-looping region of the guide roll tends to be destroyed with respect to the web width direction, while air flow balance is rather maintained with respect to the circumferential direction of the guide roll. Thus, the web is likely to move widthwise. Particularly, when the supply of compressed air is increased, the side edge portions of the web become more likely to be turned up; thus, the web becomes more likely to move widthwise.
Therefore, since the supply of compressed air must be decreased, the web fails to float sufficiently, causing rubbing between the guide roll and the web with resultant blurred printing. Further, the air outlet holes may become clogged with ink and paper dust.